Lakes of the Altiplano (Bolivia): in situ exploration of the (a)biotic Processes controlling the Aquatic biogeoCHemistry of Mercury At the Molecular and Isotopic scAle. – LA PACHAMAMA

To study the environmental chemistry and advanced transformations of contaminants, combined molecular and multi isotopic signatures should provide new information to better constrain their biogeochemical fate and ecotoxicological impact. The compound specific isotopic composition can also be relevant to quantify environmental processes and track pollution sources in complex ecosystems and provide a new dimension for environmental risk assessment. In this way, the recent advances in Hg stable isotope biogeochemistry have demonstrated meaningful variations in natural Hg isotope composition and highlighted the potential for tracing sources and quantifying Hg transformations.
The main objective of the ANR project "LA-PACHAMAMA" is to combine for the first time the information on the molecular speciation of mercury and on the isotopic composition of its related compounds, methylmercury (MeHg) and inorganic mercury (IHg), as well as the transformation extent of these chemical forms (methylation / demethylation /reduction). It is expected that such information will provide a better understanding of the complex mechanisms of regulation of toxic forms and their transfer at various interfaces (sediment / water / air) and within food webs. The originality of this project lies into the fact that most of the experiments will be conducted in situ and directly applied to the emblematic Peruvian/Bolivian hydrosystem “Titicaca - Uru Uru – Popoo”, in which the different climatic, hydrologic and anthropogenic gradients are expected to provide a set of novel and fundamental outcomes, but also highly relevant conclusions to the regional management of the metallic pollution in major aquatic environments from the Altiplano region. This extreme lake ecosystems displays unique biogeochemical features such as high altitude, significant productivity, high UV radiations and low oxygenated waters that are likely to stimulate significantly both the production and degradation of MeHg, and likely Mass Depedent and Mass Independent fractionation of Hg isotope.
The scientific and experimental strategy is to focus on process studies conducted in the field by multidisciplinary approaches among the biogeochemical problems addressed as follow:
-Perform a first assessment of the Hg contamination source and fate in the lake Titicaca hydrosystem.
-Determine the physico-chemical and hydrological factors influencing the formation, degradation and isotopic fractionation of methylmercury
-Determine the ecological and physico-chemical factors influencing the bioaccumulation, foodwebs transfer and isotopic fractionation of methylmercury
-Integrate of the molecular and isotopic information in relation to the aquatic ecosystem structures in order to provide risk assessment tools towards local and global perspectives of application.